function

1. An action performed by a device, department, or person that produces a result. Function remains more or less fixed whereas the purpose (which indicates intention or objective) generally changes. For example, the function of a hammer is to strike something nearby whereas its purpose (what to strike and why) could be anything the hammer-wielder has in mind.

2. Mathematics: A mathematical relationship in which a quantity (dependent variable) depends on or is determined by another quantity (independent variable) or quantities. The dependent variable is said to be a function of the independent variable(s).

If something is done, or something happens, to the independent variable(s), it is reflected in the dependent variable. For example, expenditure is a function of income and, for a wage earner, income is a function of two variables: per hour wage rate and number of hours worked.